The present invention is directed to a two-cycle internal combustion engine and the operation of such an engine. Such engines are used, for example, to drive various vehicles such as snowmobiles, motorcycles, personal watercraft and others.
The operation of such engines is based on the ignition of a compressed fuel-air mixture within a cylinder, with the resulting expansion of the ignited mixture driving a reciprocating piston located in the cylinder. The reciprocating movement of the piston then is used to drive the vehicle powered by the engine.
It is desirable to vary the point during the reciprocation cycle of the piston at which the fuel-air mixture is ignited, i.e. a point between "bottom dead center" and "top dead center ", to provide optimum operation of the engine. Thus, as one example the optimum point of ignition during acceleration can differ from that for a normal running operation. Because the piston usually is driven by a rotating crank shaft, the ignition point often is expressed in terms of degrees of advancement with respect to top dead center, in other words the position with respect to degrees of rotation of the rotating crank shaft ahead of the top dead center position.
Typically, different engine operating speeds, which usually are expressed in revolutions per minute, will be associated with different engine conditions. For example, higher engine speeds often are associated with acceleration. Thus, it has been considered that the point of ignition during the reciprocation cycle of the piston should be varied, depending on the engine operating speed at the particular time, and engine ignition control systems can be programmed to vary the ignition point depending on the engine speed.
Other factors can affect the optimum ignition timing. For example, an engine operating shortly after start-up may require a different relationship between ignition timing and engine speed (hereinafter "ignition pattern") than an engine that has been operating from some time. Consideration has been given in the past to a system that allows the user to switch between two different ignition patterns. This has not been completely satisfactory in optimizing engine performance.